探秘Spring的PropertyEditor - Bieber的个人页面

探秘Spring的PropertyEditor

今天无意之中一位网友咨询一个问题让我有了深入了解一下Spring的PropertyEditor机制的机会，虽然之前也大概知道些，但是都是知道它是什么，却不知道在Spring整个机制中它是如何执行的。今天就趁着中午闲暇时间看了一下Spring这方面的源码。所以这里主要是通过分析Spring的源码来了解PropertyEditor。

其实PropertyEditor是JDK里面的java.beans下面的类，是提供AWT进行渲染用的。Spring通过利用该接口，来实现Bean的属性转换器。我们在Spring的xml或者其他途径配置的bean属性都是字符串类型的值，但是对应到每个具体的属性是各种类型的，Spring通过各种PropertyEditor来对各个属性进行类型转换，在Spring中的PropertyEditor并不是直接实现PropertyEditor接口，是通过PropertyEditorSupport类屏蔽了一些Spring不需要的方法比如paintValue，从而对它们提供了默认的实现，所以Spring里面的PropertyEditor都是在PropertyEditorSupport的基础上实现的。那么先看看Spring到底提供了哪些PropertyEditor的实现，下面截取了通过IDE工具找到的实现类截图：

这里面基本涉及到了所有JDK提供的类型，知道spring提供哪些PropertyEditor之后，还得需要这些PropertyEditor是怎么嵌入Spring的。

PropertyEditorRegistry

这个是Spring框架内部将PropertyEditor嵌入Spring的方式，其中BeanWrapperImpl就是一个例子。先看看BeanWrapperImpl的类图：

可以看到BeanWrapperImpl其实就是PropertyEditorRegistry的子类。其实PropertyEditorRegistry是一个接口，做具体事情的是PropertyEditorRegistrySupport。在PropertyEditorRegistrySupport中存在一个方法createDefaultEditors，这个方法就是初始化Spring中默认PropertyEditor。下面看看哪些是Spring默认的PropertyEditor：

private void createDefaultEditors() { this.defaultEditors = new HashMap<Class<?>, PropertyEditor>(64); // Simple editors, without parameterization capabilities. // The JDK does not contain a default editor for any of these target types. this.defaultEditors.put(Charset.class, new CharsetEditor()); this.defaultEditors.put(Class.class, new ClassEditor()); this.defaultEditors.put(Class[].class, new ClassArrayEditor()); this.defaultEditors.put(Currency.class, new CurrencyEditor()); this.defaultEditors.put(File.class, new FileEditor()); this.defaultEditors.put(InputStream.class, new InputStreamEditor()); this.defaultEditors.put(InputSource.class, new InputSourceEditor()); this.defaultEditors.put(Locale.class, new LocaleEditor()); this.defaultEditors.put(Pattern.class, new PatternEditor()); this.defaultEditors.put(Properties.class, new PropertiesEditor()); this.defaultEditors.put(Resource[].class, new ResourceArrayPropertyEditor()); this.defaultEditors.put(TimeZone.class, new TimeZoneEditor()); this.defaultEditors.put(URI.class, new URIEditor()); this.defaultEditors.put(URL.class, new URLEditor()); this.defaultEditors.put(UUID.class, new UUIDEditor()); // Default instances of collection editors. // Can be overridden by registering custom instances of those as custom editors. this.defaultEditors.put(Collection.class, new CustomCollectionEditor(Collection.class)); this.defaultEditors.put(Set.class, new CustomCollectionEditor(Set.class)); this.defaultEditors.put(SortedSet.class, new CustomCollectionEditor(SortedSet.class)); this.defaultEditors.put(List.class, new CustomCollectionEditor(List.class)); this.defaultEditors.put(SortedMap.class, new CustomMapEditor(SortedMap.class)); // Default editors for primitive arrays. this.defaultEditors.put(byte[].class, new ByteArrayPropertyEditor()); this.defaultEditors.put(char[].class, new CharArrayPropertyEditor()); // The JDK does not contain a default editor for char! this.defaultEditors.put(char.class, new CharacterEditor(false)); this.defaultEditors.put(Character.class, new CharacterEditor(true)); // Spring's CustomBooleanEditor accepts more flag values than the JDK's default editor. this.defaultEditors.put(boolean.class, new CustomBooleanEditor(false)); this.defaultEditors.put(Boolean.class, new CustomBooleanEditor(true)); // The JDK does not contain default editors for number wrapper types! // Override JDK primitive number editors with our own CustomNumberEditor. this.defaultEditors.put(byte.class, new CustomNumberEditor(Byte.class, false)); this.defaultEditors.put(Byte.class, new CustomNumberEditor(Byte.class, true)); this.defaultEditors.put(short.class,http://kunmfpk.tumblr.com, new CustomNumberEditor(Short.class, false)); this.defaultEditors.put(Short.class, new CustomNumberEditor(Short.class, true)); this.defaultEditors.put(int.class, new CustomNumberEditor(Integer.class, false)); this.defaultEditors.put(Integer.class, new CustomNumberEditor(Integer.class, true)); this.defaultEditors.put(long.class, new CustomNumberEditor(Long.class, false)); this.defaultEditors.put(Long.class, new CustomNumberEditor(Long.class, true)); this.defaultEditors.put(float.class, new CustomNumberEditor(Float.class, false)); this.defaultEditors.put(Float.class, new CustomNumberEditor(Float.class, true)); this.defaultEditors.put(double.class, new CustomNumberEditor(Double.class, false)); this.defaultEditors.put(Double.class, new CustomNumberEditor(Double.class, true)); this.defaultEditors.put(BigDecimal.class, new CustomNumberEditor(BigDecimal.class, true)); this.defaultEditors.put(BigInteger.class, new CustomNumberEditor(BigInteger.class, true)); // Only register config value editors if explicitly requested. if (this.configValueEditorsActive) { StringArrayPropertyEditor sae = new StringArrayPropertyEditor(); this.defaultEditors.put(String[].class, sae); this.defaultEditors.put(short[].class, sae); this.defaultEditors.put(int[].class, sae); this.defaultEditors.put(long[].class, sae); } }

执行完这个那么BeanWrapperImpl就具备上面类型的转换功能，可能上面能够转换的类型还不能满足我们的需求，那么可以通过另一种方式将PropertyEditor注入到Spring中。

PropertyEditorRegistrar

该接口只有一个方法void registerCustomEditors(PropertyEditorRegistry registry),实现该方法就可以往传入的registry添加自定义的PropertyEditor，一般情况下传入的registry是BeanWrapperImpl的实体，所以就等于将自定义的PropertyEditor注入到BeanWrapperImpl里面。现在的问题是怎么将PropertyEditorRegistrar注入到Spring中，那么就可以将自定的PropertyEditor添加到Spring中。Spring提供了一个类专门用来将第三方的PropertyEditor注入到它里面，这个类就是CustomEditorConfigurer，先看看这个类的类图：

发现它是实现了BeanFactoryPostProcessor接口，那么将会在构造完BeanDefinition之后调用方法postProcessBeanFactory,只有整个方法是嵌入Spring的唯一途经，那么看看这个方法里面做了什么事情:

public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { if (this.propertyEditorRegistrars != null) { for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) { beanFactory.addPropertyEditorRegistrar(propertyEditorRegistrar); } } if (this.customEditors != null) { for (Map.Entry<String, ?> entry : this.customEditors.entrySet()) { String key = entry.getKey(); Object value = entry.getValue(); Class requiredType = null; try { requiredType = ClassUtils.forName(key, this.beanClassLoader); if (value instanceof PropertyEditor) { if (logger.isWarnEnabled()) { logger.warn("Passing PropertyEditor instances into CustomEditorConfigurer is deprecated: " + "use PropertyEditorRegistrars or PropertyEditor class names instead. " + "Offending key [" + key + "; offending editor instance: " + value); } beanFactory.addPropertyEditorRegistrar( new SharedPropertyEditorRegistrar(requiredType, (PropertyEditor) value)); } else if (value instanceof Class) { beanFactory.registerCustomEditor(requiredType, (Class) value); } else if (value instanceof String) { Class editorClass = ClassUtils.forName((String) value, this.beanClassLoader); Assert.isAssignable(PropertyEditor.class, editorClass); beanFactory.registerCustomEditor(requiredType, editorClass); } else { throw new IllegalArgumentException("Mapped value [" + value + "] for custom editor key [" + key + "] is not of required type [" + PropertyEditor.class.getName() + "] or a corresponding Class or String value indicating a PropertyEditor implementation"); } } catch (ClassNotFoundException ex) { if (this.ignoreUnresolvableEditors) { logger.info("Skipping editor [" + value + "] for required type [" + key + "]: " + (requiredType != null ? "editor" : "required type") + " class not found."); } else { throw new FatalBeanException( (requiredType != null ? "Editor" : "Required type") + " class not found", ex); } } } } }

发现它都调用了beanFactory的方法将配置的PropertyEditorRegistrar和customEditors注入到Spring的bean工厂里面。我们只要往spring容器中注入一个CustomEditorConfigurerBean,http://nancfpk.tumblr.com/，然后设置propertyEditorRegistrars和customEditors属性就可以将自定义的PropertyEditor注入到Spring中了。当然你也可以不用CustomEditorConfigurer类，自定义一个类实现BeanFactoryPostProcessor接口，然后按照CustomEditorConfigurer类似的路径，也可以达到目的。下面给出一个自定义PropertyEditor大致流程：

public class CustomPropertyEditor extends PropertyEditorSupport { @Override public void setAsText(String text) throws IllegalArgumentException { super.setAsText(text); } @Override public Object getValue() { return super.getValue(); } }

上面是定义了一个自定义PropertyEditor,下面需要将这个PropertyEditor注入到Spring里面中：

<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer"> <property name="customEditors"> <map> <entry key="com.xx.foo.FooPojo" value="com.xx.foo.CustomPropertyEditor"/> </map> </property> </bean>,http://chengdp.tumblr.com/;

Spring都会调用setAsText方法将该属性的字面值设置进来，然后需要根据你规定的规范转换成对应的属性对象。

下面再给出一个ClassEditor的实现，大家可以仿照这个来实现：

public class ClassEditor extends PropertyEditorSupport { private final ClassLoader classLoader; /** * Create a default ClassEditor, using the thread context ClassLoader. */ public ClassEditor() { this(null); } /** * Create a default ClassEditor, using the given ClassLoader. * @param classLoader the ClassLoader to use * (or {@code null} for the thread context ClassLoader) */ public ClassEditor(ClassLoader classLoader) { this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader()); } @Override public void setAsText(String text) throws IllegalArgumentException { if (StringUtils.hasText(text)) { setValue(ClassUtils.resolveClassName(text.trim(), this.classLoader)); } else { setValue(null); } } @Override public String getAsText() { Class clazz = (Class) getValue(); if (clazz != null) { return ClassUtils.getQualifiedName(clazz); } else { return ""; } } }